Recently, for reducing dioxins contained in the exhaust gas from a refuse incineration system, attempts are being made to measure in real time dioxins or precursors thereof contained in the exhaust gas and use the measurement values for controlling combustion of the incineration furnace. The dioxins may be measured with high-resolution GC/MS (gas chromatography/mass spectrometer). However, this method requires cumbersome pretreatment and, currently, a time of from sampling to obtaining a result needs several weeks so that it is not practical to use this method where real-timeness is required. An on-line monitor is known in which dioxins or precursors thereof contained in exhaust gas are ionized by an atmospheric pressure chemical ionization method and the resultant ions are measured by means of a three-dimensional tetrode mass spectrometer. The on-line monitor has been described in detail in Abstracts of the 11th Conference 2000 of Japan Society of Waste Management Experts, and see the literature if necessary.
However, the atmospheric pressure chemical ionization method has the following problems. First, the sensitivity for measurement of molecules which are hardly changed to negative ions is low due to its measurement principle, and therefore the method is difficult to apply to control with high precision. The ionization probability of a chemical substance to be measured is largely affected by the gas composition of an atmosphere. Thus, for determining a concentration of the chemical substance from the measured electric signal intensity by making calculation, it is necessary to use a chemical substance containing an expensive C isotope as an internal standard sample, increasing the cost for the measurement.
In the atmospheric pressure chemical ionization method, generally, a phenol is detected wherein there is a correlation between a phenol and a dioxin with respect to the concentration and a phenol has relatively high sensitivity of measurement. However, the phenol is likely to be deposited on a pipe and therefore the memory effect is remarkable, and, for achieving a measurement with high sensitivity, piping is required to be improved with some contrivances. In addition, even in cleaned exhaust gas, a phenol is disadvantageously detected due to the memory effect, thereby lowering the accuracy of the measurement. Further, when a substance which is more easily ionized than the precursor to be measured is present in the exhaust gas, such a substance is first ionized, thus making it difficult to accurately measure the substance to be measured.
A certain precursor (e.g., trichlorophenol), which is an optimal index substance of the dioxin concentration for one furnace, is not always an optimal index substance for another furnace since there may be a difference between the one furnace and another with respect to the type of furnace or the conditions for combustion, and thus, the method which can measure a single precursor has only poor general-purpose properties. In other words, a method having improved general-purpose properties advantageously can detect various types of chemical substances simultaneously if possible.